Preparation of sols



Patentea Dec. 30, 1947 @Morris. D. .Mars'h all,

Arlington, Mass, assignor .to MonsantoliChemical Company, St. Louis,

"'Mo.,;a corporation of Delaware 1 No Drawing. Originalapplication'septemberr3,

.1941, Serial No. 2,386,247, dated. ,Oct

409,434, now .Patent -No.

ober 9, 1945. Divided and this applieation..,August.28,,1945, Serial No.

Thisinve'ntion relates to the-preparationof=sols, .-'1-,1ld particularlytotiieipreparation ofsubstan- Many-anhydrous and1saltifreerorganosols;.such :assols containing:certain-alcohols,ethers, etheralcohols,esters,' ketones,.:= hydrocarbons .and the alike-as the continuous.phase.

r There-are several*knowmmethods= forsmaking .r: substantially:anhydrous organosols. .-Eor example; it is -old--to add alcohol .toaqueous-.silicic acid, and then torremove thewater :by'such means-:asdi'alysis "or" exposure in: a-.confinedspace to-t-he mdrying'actionof dry oarbonateot potashlor quickrlime. It is -also"-'-old;to-.; addglyoerinewto:a-.2.% colloidal silicic :acidrsolution with heat. andagitation, andthen to-evaporatethe water'to obtain a--c1ear-transparent;highlyrviscousmassbfcolloi-dal siIicic-acid inglycerine. R-HOWGVGI; theaproducts vprepared in the 'aboveamannerareeither of .low :concentrat-ion or of -:=low .stability- 'andithereforeare not :suitable sfor many industrialapurposes for which they:mightotherwise be .adapted.

- -It is accordingly aprimary'objectof this invention to prepare very-s-tabler-andi-highly dispersed inorganic oxide-sols .insubstantially.anhydrous A "organic solvents which are. oi -unusually.high-.conrcentrations: e.-'=g. contaimas muchwas twenty-five per centoxide-or. more. 7

- A-further-objectlof thevinvention istoprepare--sols'of'thetypedescribedeontaining either water miscible orwater-immiscible organic solvents as the continuous :phase.

A further object of the .invention-is'to. prepare substantiallyanhydrous. solseofla relatively high degree -of-concentrationeandstability containing I neither-aromatic or..aliphatic hydrocarbcnsas thecontinuous phase.

A stil-l furthenobject of the invention is tolprepare sols of theabovem'ature which eontain'only amelatively smallamount.oiinorganicsalt.

sun furtherbbjects and advantages 'of.the-in-- vention will appear.iromllthe following descripuction and appended. claims. lBeforeexplaining in FdetaiI the presentirnze'ntion, howeverj'it' is .to 'be-..understoodthat'theiinventiori 'is' not limitedin its.application..to'the.details described herein; since the..invention.iiscapable of otherembodiments ;and-.of.being practiced or carried out invarious ways. Also it is to be understoodthat thphraseology orterminology IhIilOS tf herein is for the- .purpo'se'ofdescription-'andnbt bf liinita tioiij and? it is notfintended to lmitthe invention claimed herein beyond the reduirements "of the prior-art. K The-inventionisin generalcarried out by first forming-an*aquasol containing 1 a colloidal inorganic oxideand" a disselvedinorganic' saltp-then addinga water-miscible. organic. solvent. to .theaquasol in an amount sufficient to precipitate the inorganic. salt "and.to permit substantially. com- .plete-removal .of the watenby'distillatiomjthere- 5 .after .removin'gctheprecipitated inorganic nsalt, asibylfiltration, centrifuging or the. like,.,and finally removinthe. water .by distillation.

. The above process results'in theproduction of vorganosols which aresubstantially freeof water, 410 i. e. 'contain not. more than about 4%of Water. Products containing only. traces of water. may, however,easily be obtained in accordance with the invention by subjecting .theabove sols .to a second-or third distillation which mayor may .notinvolve replacement .of-the original organic solvent withanother organicsolvent. .Although "the organic solvent initially employed. should bemiscible with. water, .the solventused to. replace it may be eitherWater-miscible. or Water-immiseib1e.

.The organic-solvent. initially employed should be of such a nature-asto.cause substantially com mete-precipitation of inorganic salts"andjshould eitherhave a. boiling pointl higher than that 25. of water,i. .e. sufficiently higher to jpermit'substantially completeremoval ofthe water by simple distillation, or itshould be capable. of forming aconstant-boiling mixture with water,. either 'by itself orin combinationwith a third .or .a plu- Q rality .of. additional components, whichmixture can then be fraction'allyorotherwise distilled ofi, leaving asthe residue. a sol containing thedesired organic liquid as thedispersing medium'or continuous phase. A most suitable solvent forforniling-a binaryLC. B. M. (constant boilingmixture) with water isnormalpropyl.alcohohwhich" not --only is highly miscible with water, but.is rela- ..tively cheap and may be readily obtained in largequantities. .Ethyl alcohol may also. be used in 49 accordance with this.invention, butas ethyl alco- .hol does notlforma satisfactory binary'C.B. M. with water for the purposes. of this invention, a third component,sucha's b'enzene',dichloroethylene, trichloroethylene, and the like, isadded, which forms a mixture capable oiboiling'ofi'as a ternary C. B. M.This-mixture is-f-raction'ally distilled to produce a sol havingsubstantially anhydrous ethyl'alc'oholas" the continuousvphase;

The sols-made by distilling constant: boiling mixtures, such'asazthosedescribedabove, cannot 1 only be madein'an'unusuallyhigh'stateof ccncentration, but are substantially f-ree of water. Thus,

"th'ey maybe. directlytmade with as little as 1% or less of 1-120.Moreover; they -may .be readily T :processed, as byreplacementytpproduce sols having relatively low boiling or high boilingwatermiscible or immiscible organic solvents as the continuous phase.For example, the ethyl or propyl alcohol in the sols prepared asdescribed above may be replaced with such organic liquids asCellosolves, high boiling alcohols, ethers, ether-alcohols, ketones,esters, aliphatic and aromati hydrocarbons and the like, by mixing theinitial alcohol sol with one or more of the above solvents anddistilling off the initial alcohol, either as such or in the form of aconstant boiling mixture. The resulting sols have been found to containeven less water than the sols prepared directl from the constant boilingmixtures.

As suitable organic solvents or liquids for replacing the initialalcohol sols may be mentioned such substances as Cellosolve, methyl andbutyl Cellosolve, the butyl and amyl alcohols, diethyl Cellosolve,diethyl Carbitol, methyl isobutyl ketone, ethyl and butyl acetate,benzene, toluene, and aliphatic hydrocarbons, such as lactol spirits.

Another method of further reducing the water content of sols formed frombinary constant boilin mixtures, such as the propyl alcohol sol preparedas described above, involves forming a ternary constant boiling mixtureby adding to the resulting sol an organic solvent, such as ben zene,dichloroethylene, and trichloroethylene and an additional quantity ofthe original organic solvent, and then fractionally distilling theresulting ternary mixture. The distillation product is an organosolcontaining only a trace of water. Thus, in the case of propyl alcohol itis possible to distill ofi both binary and ternary constant boilingmixtures with the result that sols having this alcohol as the continuousphase may be readily made containing very minute amounts of water.

The sols prepared from ternary constant boiling mixtures and containingonly a trace of water, such as the propyl alcohol and like sols preparedas described immediately above, may be readily converted to solscontaining water-immiscible organic solvents as the continuous phase.For example, the propyl alcohol in such sols may be replaced by tolueneor other hydrocarbons by merely mixing the hydrocarbon with thesubstantially water free alcohol sol and distilling the resultingmixture. Sols of this nature are ordinarily very difficult to obtain,but may be readily prepared in accordance with the above method.

The organic solvent or liquid employed should be added to the aquasol insufficient amounts not only to precipitate the inorganic salt containedtherein, but to prevent gelation during the early stages of thedistillation during which water is removed, and to permit substantiallycomplete removal of the water. This usually results in the formation ofan intermediate organo-aquasol containing about 3% silica.

The aquasols treated or used in connection with the above processes maybe prepared in various ways. In the case of silica sol, for example,they are preferably prepared by reacting an aqueous solution of sodiumsilicate with dilute sulfuric acid in suitable proportions. Any othersuitable method may however be employed, dependin upon the particularoxide sol which it is desired to prepare.

In general, it is preferable to use aquasols having a high concentrationof the colloidal oxide in connection with the processes of this inven- 4tion, as this permits the use of less organic solvent than wouldotherwise be required to precipitate out the inorganic salt and alsorequires less distillation to remove water.

It is also usually preferable, particularly in the case of silica sols,to prepare the aquasol and to precipitate the salt at temperatures ofnot above 15 C. Moreover, it is usually preferable to prepare and use anaquasol having a pH of between 2 and 4 to insure maximum stabilityduring the preparation of the organosols. However, the invention shouldnot be limited in these respects, as it is possible to obtain stable andsubstantially anhydrous sols of high concentration without resorting totemperatures below normal, and withoutoperating in the above mentionedpH range.

A more complete and thorough understanding of the invention will beobtained from the following examples:

Example I .--Three hundred fifty-eight pounds of sodium silicatecontaining 28.7% SiOz, 8.9% NazO and 62.4% H2O are diluted with onehundred sixty-two pounds of water. This mixture is then added to onehundred sixty-three and one-half pounds of 31% sulfuric acid and themass is agitated to distribute the silicate throughout the acid. Themixing is carried out in a suitable acid resistant apparatus at atemperature of about 15 C., and results in a silica sol having a pH ofabout 2.5. One thousand three hundred and seventy-five pounds ofCellosolve are then added to the sol gradually with stirring, whilemaintaining the temperature at about 15 C. This causes precipitation ofthe inorganic salt, which is then removed by filtering or centrifuging.To the clear sol one thousand five hundred and forty pounds ofadditional Cellosolve are added so that the SiOz content is reduced toabout 3%. The sol is then distilled in a lead still equipped with astirrer and a fractionating column, the distillation being discontinuedwhen the sol in the still is substantially free of water and containsabout 25% SiOz.

Example I I .Three hundred fifty-eight pounds of sodium silicatecontaining 28.7% S102, 8.9% NazO and 62.4% H2O are diluted with onehundred sixty-two pounds of water. This mixture is then added to onehundred sixty-three and onehalf pounds of 31% sulfuric acid and the massis agitated to distribute the silicate throughout the acid. The mixingis carried out in a suitable acid resistant apparatus at a temperatureof about 15 C., and results in a silica sol having a pH of about 2.5.One thousand three hundred and seventy-five pounds of normal propylalcohol are then added to the sol gradually with stirring whilemaintaining the temperature at about 15 C. This causes precipitation ofsubstantially all of the inorganic salt, which is then removed byfiltering or centrifuging. To the clear sol one thousand five hundredand forty pounds of additional normal propyl alcohol are added, whichreduces the SiOz content to about 3%. The sol is then distilled in alead still equipped with a stirrer and a fractionating column. Duringthe distillation the refluxing ratio is maintained in such a manner asto obtain 73% propanol in the first 50% of the distillate, about 92%propanol in the next 20% of the distillate, and about 99% propanol inthe last 30%, which leaves as a residue a sol containing about 25% SiO2.

Example III. Three hundred fifty-eight po nds oi sodium silicatecontaining 28.7% SiOa,

hundred 'sixty t-wo poundsof-water. This mixtare is theniadded to onehundred sixty-three and one-hal'ipounds of 3 1 %"sulf-uri'c-; acid andthe mass is agitated to distribute the silicate throughout the acid;Themixing is carried out in suitable acid resistant apparatus at atemperature ofabout'l5-C., andresults in a silica sol having a pH ofabout 2;5. One thousand three hundred and seventy-five pounds of ethylalcohol (containing about 92% C2H5OH by weight) are then added to thesol gradually with stirring, while maintaining the temperature at about15 C. This causes precipitation of sub stantially all of the inorganicsalt, which is removed by filtering or centrifuging. To the clear solone thousand five hundredana forty pounds of'additional alcoholareadded, which reduces theSiOz contentto about-3%. The sol is thendistilled in a lead still equipped with a stirrer and a fractionatingcolumn having 28 theoretical plates. Eight hundred and ten pounds ofbenzol are gradually introduced into the top of the column during thefirst part of the run. The column is operated at capacity and thetemperature at the top is maintained at 65 C. by proper reflux control,until all of the lower aqueous layer has been separated and removed. Ahigh reflux ratio is then maintained until all the benzol-alcoholfraction has been removed. Substantially anhydrous alcohol is thenremoved at a rapid rate until the sol in the still contains an S102content of about 25%.

Example IV. -A mixture containing one part by weight of the 25% propylalcohol sol prepared in accordance with Example II, two parts by weightof anhydrous normal propanol and one and one-quarter parts by weight ofbenzol is distilled in a distillation apparatus equipped with a stirrerand a fractionating column having 28 theoretical plates, which resultsfirst in the removal of the water layer which forms and then in theremoval of the C. B. M. containing normal propanol and benzol. Thedistillation is continued until the final dehydrated sol, containingonly a trace of water, has been concentrated to a 25% SiOz content.

Example V.--Five parts by weight of toluene are added to one part byweight of the normal propanol sol containing 25% SiOz obtained inaccordance with Example IV. The resulting mixture is then distilled in adistillation apparatus provided with a, stirrer and a fractionatingcolumn until all the normal propyl alcohol is removed as a C. B. M. andthe resulting toluene sol contains an SiOz content of about 15%.

Example VI.-Two and one-half parts by weight of butyl acetate are addedto one part by weight of the normal propyl alcohol sol containing 25%SiOz obtained in accordance with Example II. The mixture is thendistilled in a distillation apparatus provided with a stirrer and afractionating column until all the normal propyl alcohol is removed,whereupon the distillation is continued until the resulting butylacetate sol residue contains about 25% SiOz.

As indicated by the above examples, the method of this invention notonly permits the production of highly concentrated and stableorgano'sols which are substantially free of water, but they render itpossible to prepare substantially salt free sols having a wide varietyof organic solvents as the continuous phase, without resorting tocumbersome and time consuming methods of removing the salt, such asdialysis or 6 the like. The; organic solvents used-or present inthe'finalj s01 may" be either water-miscible or water-immiscible, highboiling or low boiling.

Moreover, they may compriseor consist of such hydrocarbons or mixturesof hydrocarbons, as benzene, toluene, lactol spirits or the like, whichheretofore it has not been possible to successfully prepare as sols ofthe type described.

Although the bove examples refer solely to the preparation oforgariosols'containing an individual organic solvent, it should beunderstood thatthe invention is not limited to such sols, and

thatsols may also be prepared containing mixtures of organic solvents.'For example, an organosol may beprepared directly, using mixture ofwater-miscible solvents instead 'of just one, or the solvent or solventsin the initial organosol may be replaced by any suitable mixture oforganic solvents, which in such case may be either water-miscible orwater-immiscible.

The term organic solvents employed herein and in the appended claims isintended to refer to the type of solvents commonly employed in the fieldof coating compositions, such as varnishes, lacquers, and the like, andcommonly understood by chemists as suitable for such purposes. The termis also intended to include, however, alcohols which are usually notemployed as solvents in the coating art.

The term Cellosolve represents the mono ethyl ether of ethylene glycol,while methyl, ethyl, butyl and diethyl Cellosolve represents the methyl,ethyl, butyl and diethyl ethers of ethylene glycol respectively. Theterm lactol spirits represents a product consisting of homogeneousclosely fractionated portions of petroleum crude oil which are derivedfrom petroleum by distillation and constitute a mixture of hydrocarbonshaving an evaporation rate similar to or close to that of toluene. Theproduct has a specific gravity of .7313 at 60 F. and the following A. S.T. M. distillation range:

Per cent Distilled Temperature F. Initial boiling point 200 50%Distilled 220 Distilled 240 This application is a division of myco-pending application Serial No, 409,434, filed September 3, 1941, nowPatent No, 2,386,247, granted October 9, 1945, which is acOntinuation-in-part of application Serial No. 272,404, filed May 8,1939, and granted June 9, 1942, as Patent No. 2,285,449.

What I claim is:

1. The method of preparing a stable and substantially anhydrousorganosol composed of colloidal silica and butyl acetate which comprisesforming an aquasol containing colloid-a1 silica and a dissolvedinorganic salt, adding ethyl alcohol to said aquasol in an amountsufiicient to precipitate the inorganic salt, removing the precipitatedinorganic salt, adding additional ethyl alcohol and adding benzene inamounts sufficient to permit substantially complete removal bydistillation of the water, the alcohol being added in an amountsuliicient to permit substantially complete removal of the benzene bydistillation, removing the water and the benzene by distillation, andthen adding an organic solvent selected from the group consisting ofbutyl alcohol and butyl acetate and removing the ethyl alcohol bydistillation.

2. The method of preparing a stable and sub-v stantially anhydrousorganosol composed of colloidal silica and butyl acetate which comprisesforming an aquasol containing colloidal silica and a dissolved inorganicsalt, adding ethyl alcohol to said aquasol in an amount sufficient toprecipitate the inorganic salt, removing the precipitated inorganicsalt, adding additional ethyl alcohol and adding benzene in amountssurficient to permit substantially complete removal by distillationof-the water, the alcohol being added in an amount sufiicient to permitsubstantially complete removal of the benzene by distillation, removingthe water and the benzene by distillation, and then adding buty1 acetateand removing the ethyl alcohol by distillation.

3. The method of preparing a stable and substantially anhydrousorganosol composed of colloidal silica and butyl alcohol which comprisesforming an aquasol containing colloidal silica and a dissolved inorganicsalt, adding ethyl al- REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,386,247 Marshall Oct. 9, 19452,375,738 White May 8, 1945

